My sister recently got pregnant and is acting all righteous?

I'm beyond happy for my sister. I love the fact she's going to have a baby but lately she has been acting like she's never done anything wrong in her life. She had a pretty wild strike but not that she's pregnant in her eyes its been erased. She use to smoke and drink every weekend. But now she looks down on people that do the same things she use to do. I don't understand why she's like this I've never been pregnant so I have no idea what she's going through. I just don't understand why she became to jugdey.